1. Field of the Invention
The present invention relates to a chemical amplification resist copolymer and a resist composition containing it. More particularly, the present invention relates to a photoresist copolymer, which is useful as a matrix resin to form micro patterns, and a chemical amplification resist composition based on the copolymer, which makes it possible to perform a sub-micro lithography process using a deep UV such as a KrF excimer laser or an ArF excimer laser, an X ray such as synchrotron radiation, or charged particle beams such as electron beams.
2. Description of the Prior Art
Certainly, the recent thrust into the high integration of semiconductor devices is greatly based on advances in microlithography. For example, ultra-fine patterns as small as sub-microns, e.g. 0.2 microns or less, in size, are required for the fabrication of ultra-LSI. Now, the light sources used to form the fine patterns become increasingly shorter in wavelength, for example, from g-line or i-line, to deep UV light, including KrF excimer lasers and ArF excimer lasers, further to X-rays, and finally to electron beams.
With near UV light, such as g-line or i-line, which is used in conventional lithography, micro patterns as small as quarter microns (0.25 microns) are virtually impossible to realize. Such a micro pattern requires shorter wavelengths which belong to deep UV excimer lasers, X rays, and electron beams. Of them, KrF and ArF excimer lasers occupied the attention of the researchers in expressing such exquisiteness, and were developed as a light source, requiring novel photoresists. Now, chemical amplification photoresists are prevalently used for deep UV light.
A chemical amplification resist composition suitable for deep UV light fundamentally comprises a polymer with an acid-dissociable functional group, a compound which generates an acid (hereinafter referred to as "photoacid generator"), and a solvent, and avails itself of chemical amplification effect in lithography.
Most of the chemical amplification resists used for KrF excimer lasers are based on phenolic resins which, however, are found to be unsuitable for utilizing an ArF excimer laser because their aromatic rings absorb the light.
As an alternative, polyacrylate derivatives appeared to avoid such absorption. Polyacrylate derivatives show little absorbance at 193 nm, but suffer from a great disadvantage in that they are far inferior in dry etch resistance. Recently, much effort has been made to overcome the disadvantage, including the introduction of alicyclic derivatives into polyacrylate. The introduction of alicyclic derivatives certainly brings about an improvement in dry etch resistance, but causes a significant problem in a developing process because their hydrophobicity has a negative influence on the affinity for developing solutions.
It is known that copolymers of maleic anhydride and olefin can be used as matrix resins which show not only hydrophilicity, but also etch resistance. In the copolymers, maleic anhydride, responsible for hydrophilicity, serves as a promoter which enables the copolymerization with olefinic monomers to be accomplished at low temperatures at low pressures.